Peripheral sensors for occupant protection systems usually use current interfaces (e.g. PAS4, PSI5) to transfer sensor data to a central control device (ECU) in a vehicle. In current interfaces of the latest generation (PSI5), bus operation with multiple sensors on one receiver is made possible by synchronization. For the synchronization function, a working clock signal in the form of a voltage pulse is generated by the central control device (ECU); said pulse is detected by the sensors on the bus and characterizes the beginning of a new cycle for data transfer. This voltage pulse is referred to as a “synchronization pulse” and is produced with the aid of current sources and current sinks that respectively charge and discharge the bus load. This voltage pulse is typically repeated every 500 μs.
In order for a synchronous bus system to function with one sensor or with multiple sensors, it is important that the synchronization pulse have a specific shape and exhibit a specific time-related behavior for all possible bus configurations and under all possible operating conditions. A trapezoidal synchronization pulse having a predefined edge slope is therefore used as a rule in known synchronous bus systems. The edge slope here is between an edge slope of a first characteristic curve which represents a lower limit, and an edge slope of a second characteristic curve which represents an upper limit. During synchronous bus operation, the trapezoidal shape of the synchronization pulse results in increased electromagnetic emission (EMC) in the signal transfer frequency spectrum because of the large proportion of harmonics. This can be counteracted to a certain degree, for example, by way of a synchronization pulse that has a trapezoidal shape having four rounded corners.
The unexamined German application DE 10 2009 001 370 A1 describes a receiving device for accepting current signals, a circuit assemblage having such a receiving device, and a method for transferring current signals via a bus system. The receiving device described encompasses at least two bus connector devices for the acceptance of current signals of multiple transmitters, each bus connector device being embodied for connection to at least one respective bus connection, and a control device for outputting synchronization pulses to the bus connector devices for synchronization of the transmitters. The bus connector devices output the synchronization pulses to the multiple transmitters with at least one time offset with respect to one another, the synchronization pulses each having a trapezoidal shape having rounded corners.